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Re: [EnergyPlus_Support] warm-up time

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] warm-up time
From: Rick Strand <rkstrand@xxxxxxxx>
Date: Mon, 15 Mar 2004 10:50:05 -0600
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Yes, it would be possible to modify the weather file as Ned mentioned.  I 
think this would be preferred over any other approach since you will know 
where the conditions started and the building thermal mass will have an 
adequate amount of "history" to be realistic.

It is possible, but not advisable, to reduce the number of warmup days by 
modifying the maximum number of warmup days.  In the BUILDING object in the 
input file (.idf), change the maximum number of warmup days and this will 
force E+ to start the simulation sooner if this number is low.  Note that 
this number must be greater than zero--so one warmup day is an absolute 
minimum.  Again, I would not recommend this approach since, depending on 
the thermal mass of your building, the results may not be very dependable.

Rick Strand

At 10:15 PM 3/13/2004, you wrote:
>hi:
>since EPlus uses the first day of the simulation to perform its warm-up 
>till it reaches convergence and then simulates for the rest of the days - 
>is there any way of controling this warm-up period/time...? can one enter 
>ZERO warm-up days...?
>OR as ned mentioned - use a cool period before the hotter days to see how 
>my building responds to a quick warm-up (is the only way). as this will 
>require altering the weather file...!
>thank you,
>~m
>
>Rick Strand <rkstrand@xxxxxxxx> wrote:
>As Ned and Dru have already mentioned, E+ does have a warmup period during
>which the program will iterate on the same day until it reaches
>"convergence".  For a design day environment, E+ will use the design day
>and repeat it until it reaches "steady periodic" conditions.  For a weather
>environment, E+ will use the first day of the weather file for the warmup
>period.  Once convergence is reached in any of these cases, it will then
>start the simulation time clock.  Note that it reinitializes temperature
>histories between different weather environments (individual design days or
>weather files) to the same starting initial condition before it starts the
>iterative warmup process.
>
>As Ned suggested, if one wants to see how the building reacts to several
>days of extreme conditions, add an additional "normal" day to the weather
>period.  The results should show the temperatures/loads drift, with the
>amount of drift obviously a function of building type, materials, location,
>weather, etc.
>
>Rick Strand
>
>At 08:53 AM 3/11/2004, Edward Lyon wrote:
> >As I understand the startup of an E+ calculation, the program must
> >iterate to a repeatable starting condition before moving into the actual
> >calculation.  Consequently, if you try to model single days (like just a
> >design day), your model will always look like the conditions have been
> >the same for a long time.  To see what you want, you probably need to
> >calculate several days with the first days being your cool weather and
> >the last days being your hot weather.  You should then see the building
> >respond to a quick warmup.
> >
> >Ned Lyon
> >
> >Senior Project Manager
> >Simpson Gumpertz & Heger Inc.
> >
> >41 Seyon Street
> >Building #1, Suite 500
> >Waltham, MA  02453
> >
> >Phone:  781-907-9000
> >Fax:  781-907-9009
> >
> > >>> mohitmehta1@xxxxxxxxx 03/11/04 12:38 AM >>>
> >
> >hi:
> >
> >if am running a simulation of a high mass NV building between aug 14 -
> >17 (4 hot days) - shouldn't the building take a few hours or days to
> >warm up? like indoor and outdoor temperatures starting out the same on
> >the first day (aug 14), and indoor air temperatures climbing gradually
> >over the four-day period; finally balancing out? it appears that the
> >mass starts out as preheated (warmed/cooled). does it use 3-4 warm-up
> >days before the days that i am looking at are reported?
> >
> >thank you.
> >
> >~m
> >
> >
> >---------------------------------
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References:
- Re: [EnergyPlus_Support] warm-up time
  - From: Rick Strand
- Re: [EnergyPlus_Support] warm-up time
  - From: Mohit Mehta

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